An isolation valve is used to isolate a formation penetrated by a wellbore from fluids and pressures in the wellbore above the isolation valve (or nearer the earth's surface). In some circumstances, it is desirable to install one isolation valve above another isolation valve.
If a lower isolation valve is mechanically operated by means of a shifting tool, the lower isolation valve can have the shifting tool remaining therein (for example, to open the valve) after the upper isolation valve has been installed (along with a packer, other completion equipment, etc.). The shifting tool left in the lower isolation valve can restrict flow through the valve. The lower isolation valve could be below a mechanically, remotely or otherwise operable isolation valve.
Therefore, it will be appreciated that improvements are continually needed in the arts of constructing isolation valves and actuating isolation valves in a well.